need opinions...

[taacrmachine]

I'm new to mumsnet so I'm not sure about all the abbreviations, here it goes.
looking after two boys, 2 and 4 1/2.
The 2yr old starts crying/having a tantrum/screaming for parents if he is asked/told not to do something or if anything he does is discussed with him. I try to keep any conversation (unless about something dangerous) light, smiley and calm, but he still goes off the deep end. Anyone have any idea about how to stop this reaction, feel like any contradiction I make to his behaviour makes me out to be a monster!
The 4 yr old is having some behavioural issues in school, he started in september and theres been a few incidents already. when with me, he ignores me, insists he is right when I ask him to do something, along with various other forms of back chatting, violence towards his brother (biting, hitting etc). He can be well behaved, I've seen it and rewarded it but as soon as he is praised for good behaviour, he does something horrendous.
Not sure if he was like this with his old childminder, if he was, she shielded his parents from it.
I know what plan of action I would suggest to his parents but I would love some opinions, as you can imagine it is a touchy subject.

[chobbler]

have you looked at 1-2-3 magic? I used it with 30+ kids at the preschool I worked at, with one or two minor problems it was hugely successful.

[Octaviapink]

I'd suggest speaking to his old childminder. Are the two boys siblings? You might try posting this in the childminder section, too.

[taacrmachine]

hi, yes apparently 1-2-3 approach is supposed to work according to the parents, but i think this was with the old childminder. they aren't phased by me doing it.
yes I'm a nanny to two boys who are siblings, I was thinking about speaking to the old childminder but I'm not sure it would be appropriate due to the relationship between her and the family.
I've posted this in the nannies and childminders section too, thanks for your help :)